Shadowrun Toolbox is protected by the GNU General Public License v3.0 license, which you can find on the GNU website. This is a complex text meant to protect the software writers.

Here you can read that anyone can download , use, copy, transfer, sell, even adjust the software without restrictions... provided that you don't alter the license.

The source code is open to all and may even be used in other software, provided that this software also uses the GNU GPL license.